Electrophotographic photosensitive material containing m-phenylenediamine compound

ABSTRACT

Disclosed is an electrophotographic photosensitive material containing in a photosensitive layer an m-phenylenediamine compound represented by the following general formula [I]: ##STR1## wherein R 5 , R 6 , R 7  and R 8  are groups substituted at meta-positions to the nitrogen atoms and represent a hydrogen atom, an alkyl group, an alkoxyl group or a halogen atom, with the proviso that at least two of R 5 , R 6 , R 7  and R 8  represent an alkyl group, alkoxyl group or a halogen atom, and R represents a hydrogen atom, an alkyl group, an alkoxyl group or a halogen atom. 
     This meta-substituted m-phenylenediamine compound of general formula [I] is hardly crystallized in a resin but is sufficiently dissolved in the resin, and therefore, the concentration of the compound in the resin can be increased and the mobility can be enhanced. Accordingly, an electrophotographic photosensitive material having an increased sensitivity can be provided.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an electrophotographic photosensitivematerial comprising an m-phenylenediamine compound as a charge transportsubstance.

(2) Description of the Related Art

An organic photosensitive material which has a good processability, isadvantageous from the viewpoint of the manufacturing cost and has alarge freedom of design of functions is recently used as anelectrophotographic photosensitive material in an imageforming apparatussuch as a copying machine. Especially, photosensitive layers comprisinga charge generating material capable of generating charges underirradiation with light and a charge transport material for transportingthe generated charges, for example, function-separated single-layer typephotosensitive materials comprising a charge generating material, acharge transport material and a binder resin, and function-separatedelectrophotographic photosensitive materials having a laminate typephotosensitive layer having a laminate structure comprising a chargegenerating layer containing a charge generating material as describedabove and a charge transport layer containing a charge transportmaterial as mentioned above, have been proposed.

The Carlson process is widely used for forming a copied image by usingan electrophotographic photosensitive material. The Carlson processcomprises, in principle, the charging step of uniformly charging aphotosensitive material by corona discharge, the light-exposure step ofexposing the charged photosensitive material imagewise to light to forman electrostatic latent image corresponding to an original image, thedeveloping step of developing the electrostatic latent image with adeveloper containing a toner to form a toner image, the transfer step oftransferring the toner image to a substrate such as a paper sheet, thefixing step of fixing the toner image transferred onto the substrate,and the cleaning step of removing the toner left on the photosensitivematerial after the transfer step. In order to form a high-quality imagein this Carlson process, it is required that the electrophotographicphotosensitive material should be excellent in charging characteristicsand photosensitive characteristics, and the residual potential after thelight exposure should be low.

In the above-mentioned function-separated electrophotographicphotosensitive material, the electric characteristics and photosensitivecharacteristics of the photosensitive material are greatly influenced bythe characteristics of the charge generating material and chargetransport material. Accordingly, various substances have been examined,and polyvinyl carbazoles, oxadiazole compounds, pyrazoline compounds andhydrazone compounds have been proposed as the charge transport material.

However, in these charge transport materials, the drift mobilityindicating the charge transport capacity is relatively small. Moreover,the dependency of the drift mobility on the electric field intensity islarge, and therefore, the migration of charges in a low electric fieldis small and cancellation of the residual potential is difficult.Moreover, these charge transport materials are readily deterioratedunder irradiation with ultraviolet rays and the like.

It is known that the electric field dependency of the drift mobility issmall in the triphenylamine type charge transport material. For example,U.S. Pat. No. 3,265,496 proposes N,N,N',N'-tetraphenylbenzidine,N,N,N',N'-tetraphenyl-1,4-phenylenediamine andN,N,N',N'-tetraphenyl-1,3-phenylenediamine. However, these chargetransport materials are still defective in that the sensitizing effectis low in the ordinary application and if the amount added is increased,crystallization is often caused. Therefore, these charge transportmaterials cannot be put into practical use.

For overcoming this defect, we previously proposed m-phenylenediaminecompounds, in which phenyl groups ofN,N,N',N'-tetraphenyl-1,3-phenylenediamine can optionally besubstituted, so far as the substitution is possible (see Japanese PatentApplication No. 62-301703).

Certain improvements can be attained by introduction of substituents,but it has been found that the improvements are still insufficient.

In general, the characteristics of an electrophotographic photosensitivematerial are greatly influenced by the photoconductive material used,though the influences differ more or less according to the object andpreparation process.

SUMMARY OF THE INVENTION

Under this background, we made research and as the result, it was foundthat if, of the foregoing m-phenylene-diamine compounds, a compound inwhich respective substituents are located at meta-positions to nitrogenatoms with respect to phenylene groups is selected and used for thepreparation of an electrophotographic photosensitive material, thiscompound is hardly crystallized in a binder resin.

It is therefore a primary object of the present invention to provide aphotoconductive substance which is hardly crystallized in a resin andalso provide a high-sensitivity electrophotographic photosensitivematerial comprising this photoconductive substance.

More specifically, in accordance with the present invention, there isprovided an electrophotographic photosensitive material containing in aphotosensitive layer an m-phenylenediamine compound represented by thefollowing general formula [I]: ##STR2## wherein R⁵, R⁶, R⁷ and R⁸ aregroups substituted at meta-positions to the nitrogen atoms and representa hydrogen atom, an alkyl group, an alkoxyl group or a halogen atom,with the proviso that at least two of R⁵, R⁶, R⁷ and R⁸ represent analkyl group, alkoxyl group or a halogen atom, and R represents ahydrogen atom, an alkyl group, an alkoxyl group or a halogen atom.

In the photosensitive material of the present invention, the compound ofgeneral formula [I] is incorporated as the charge transport material ina binder resin. This compound is poor in the symmetry of the molecularstructure, and the intermolecular mutual action is small. This meansthat the mutual action with a resin is large, and therefore, thecompound is hardly crystallized in a resin constituting a photosensitivelayer. Accordingly, it is possible to increase the concentration of thecompound in the resin, and if this compound is selected and used as thecharge transport material, a charge transport material-richphotosensitive material can be formed and the sensitivity can beincreased because of increase of the electron mobility in thephotosensitive layer.

Namely, the above-mentioned object can be attained by anelectrophotographic photosensitive material comprising anelectroconductive substrate and, formed thereon, a photosensitive layercontaining an m-phenylenediamine compound of general formula I.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The m-phenylenediamine compound used in the present invention isrepresented by general formula [I]. As the alkyl group for R⁵, R⁶, R⁷and R⁸, there can be mentioned lower alkyl groups having 1 to 6 carbonatoms, such as a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, an isobutyl group, a tert-butyl group, apentyl group and a hexyl group. As the alkoxyl group, there can bementioned lower alkoxyl groups having 1 to 6 carbon atoms in the alkylportion, such as a methoxy group, an ethoxy group, a propoxy group, anisopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxygroup, a pentyloxy group and a hexyloxy group.

Specific examples of the m-phenylenediamine compound of general formula[I] used in the present invention are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                         ##STR3##                      (I)                                            R        R.sup.5  R.sup.6    R.sup.7                                                                              R.sup.8                                   ______________________________________                                        OC.sub.2 H.sub.5                                                                       OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          C.sub.2 H.sub.5                                                                        C.sub.2 H.sub.5                                                                        C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      C.sub.2 H.sub.5                           C.sub.3 H.sub.7                                                                        C.sub.3 H.sub.7                                                                        C.sub.3 H.sub.7                                                                          C.sub.3 H.sub.7                                                                      C.sub.3 H.sub.7                           C(CH.sub.3).sub.3                                                                      C(CH.sub.3).sub.3                                                                      C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    C(CH.sub.3).sub.3                         OCH.sub.3                                                                              OCH.sub.3                                                                              OCH.sub.3  OCH.sub.3                                                                            OCH.sub.3                                 OC.sub.2 H.sub.5                                                                       OC.sub.2 H.sub.5                                                                       OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     OC.sub.2 H.sub.5                          OC.sub.2 H.sub.5                                                                       H        CH.sub.3   CH.sub.3                                                                             H                                         OC.sub.2 H.sub.5                                                                       C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           OC.sub.2 H.sub.5                                                                       O(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         OC.sub.2 H.sub.5                                                                       OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 CH.sub.3 CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  C(CH.sub.3).sub.3                                                                      CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  OCH.sub.3                                                                              CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  OC.sub.2 H.sub.5                                                                       CH.sub.3 CH.sub.3   CH.sub.3                                                                             CH.sub.3                                  CH.sub.3 CH.sub.3 H          H      CH.sub.3                                  CH.sub.3 CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  CH.sub.3 CH.sub.3 C.sub.3 H.sub.7                                                                          C.sub.3 H.sub.7                                                                      CH.sub.3                                  CH.sub.3 CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  CH.sub.3 CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  CH.sub.3 CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  CH.sub.3 H        CH.sub.3   CH.sub.3                                                                             H                                         CH.sub.3 C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           CH.sub.3 C.sub.3 H.sub.7                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.3 H.sub.7                           CH.sub.3 C(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         CH.sub.3 OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 CH.sub.3 OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          C.sub.2 H.sub.5                                                                        CH.sub.3 H          H      CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 C.sub.3 H.sub.7                                                                          C.sub.3 H.sub.7                                                                      CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  C.sub.2 H.sub.5                                                                        CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  C.sub.2 H.sub.5                                                                        H        CH.sub.3   CH.sub.3                                                                             H                                         C.sub.2 H.sub.5                                                                        C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           C.sub.2 H.sub.5                                                                        C.sub.3 H.sub.7                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.3 H.sub.7                           C.sub.2 H.sub.5                                                                        C(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         C.sub.2 H.sub.5                                                                        OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 C.sub.2 H.sub.5                                                                        OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          C.sub.3 H.sub.7                                                                        CH.sub.3 H          H      CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 C.sub.3 H.sub.7                                                                          C.sub.3 H.sub.7                                                                      CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  C.sub.3 H.sub.7                                                                        CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  C.sub.3 H.sub.7                                                                        H        CH.sub.3   CH.sub.3                                                                             H                                         C.sub.3 H.sub.7                                                                        C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           C.sub.3 H.sub.7                                                                        C.sub.3 H.sub.7                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.3 H.sub.7                           C.sub.3 H.sub.7                                                                        C(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         C.sub.3 H.sub.7                                                                        OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 C.sub.3 H.sub.7                                                                        OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          C(CH.sub.3).sub.3                                                                      CH.sub.3 H          H      CH.sub.3                                  C(CH.sub.3).sub.3                                                                      CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  C(CH.sub.3).sub.3                                                                      CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  C(CH.sub.3).sub.3                                                                      CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  C(CH.sub.3).sub.3                                                                      CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  C(CH.sub.3).sub.3                                                                      H        CH.sub.3   CH.sub.3                                                                             H                                         C(CH.sub.3).sub.3                                                                      C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           C(CH.sub.3).sub.3                                                                      C(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         C(CH.sub.3).sub.3                                                                      OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 C(CH.sub.3).sub.3                                                                      OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          OCH.sub.3                                                                              CH.sub.3 H          H      CH.sub.3                                  OCH.sub.3                                                                              CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  OCH.sub.3                                                                              CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  OCH.sub.3                                                                              CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  OCH.sub.3                                                                              CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  OCH.sub.3                                                                              H        CH.sub.3   CH.sub.3                                                                             H                                         OCH.sub.3                                                                              C.sub.2 H.sub.5                                                                        CH.sub.3   CH.sub.3                                                                             C.sub.2 H.sub.5                           OCH.sub.3                                                                              C(CH.sub.3).sub.3                                                                      CH.sub.3   CH.sub.3                                                                             C(CH.sub.3).sub.3                         OCH.sub.3                                                                              OCH.sub.3                                                                              CH.sub.3   CH.sub.3                                                                             OCH.sub.3                                 OCH.sub.3                                                                              OC.sub.2 H.sub.5                                                                       CH.sub.3   CH.sub.3                                                                             OC.sub.2 H.sub.5                          OC.sub.2 H.sub.5                                                                       CH.sub.3 H          H      CH.sub.3                                  OC.sub.2 H.sub.5                                                                       CH.sub.3 C.sub.2 H.sub.5                                                                          C.sub.2 H.sub.5                                                                      CH.sub.3                                  OC.sub.2 H.sub.5                                                                       CH.sub.3 C(CH.sub.3).sub.3                                                                        C(CH.sub.3).sub.3                                                                    CH.sub.3                                  OC.sub.2 H.sub.5                                                                       CH.sub.3 OCH.sub.3  OCH.sub.3                                                                            CH.sub.3                                  OC.sub.2 H.sub.5                                                                       CH.sub.3 OC.sub.2 H.sub.5                                                                         OC.sub.2 H.sub.5                                                                     CH.sub.3                                  ______________________________________                                    

The position of the substituent R is not particularly critical, and theposition of the substituent R is, for example, the 5-position.

The meta-substituted compound of general formula [I] used in the presentinvention can be synthesized according to various processes. Forexample, the metasubstituted compound can be synthesized according tothe process represented by the following reaction formula: ##STR4##

More specifically, resorcinol of formula (A) is reacted with m-toluidineof formula (B) in the presence of iodine in a nitrogen current to obtainN,N'-di(3-tolyl)-1,3-phenylenediamine of formula (C). Then,N,N'-di(3-tolyl)-1,3-phenylenediamine is reacted with iodotoluene offormula (D) in the presence of potassium carbonate and powdery copperunder reflux in nitrobenzene to obtainN,N,N',N'-tetra(3-tolyl)-1,3-phenylenediamine of formula (E).

The electrophotographic photosensitive material of the present inventionis characterized in that a photosensitive layer containing anm-phenylenediamine compound represented by general formula [I] is formedon an electroconductive substrate. The present invention can be appliedto either a function-separated single-layer photosensitive materialcontaining a charge generating material and a charge transport materialin at least one layer formed on an electroconductive substrate, or afunction-separated laminate photosensitive material comprising at leasta charge generating layer and a charge transport layer, which arelaminated on an electroconductive substrate. The compound of generalformula [I] can be used in combination with known other charge transportmaterial in the present invention. Known electron attractive compoundsand electron donative compounds can be used as the other chargetransport material. As the electron attractive compound, there can bementioned, for example, tetracyanoethylene, 2,4,7-trinitro-9-fluorenone,2,4,8-trinitrothioxanthone, 3,4,5,7-tetranitro-9-fluorenone,dinitrobenzene, dinitroanthrathene, dinitroacrydine, nitroanthraquinone,dinitroanthraquinone, succinic anhydride, maleic anhydride anddibromomaleic anhydride.

As the electron donative compound, there can be mentioned, for example,oxadiazole compounds such as2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, styryl compounds such as9-(4-diethylaminostyryl)anthrathene, carbazole compounds such aspolyvinyl carbazole, pyrazoline compounds such as1-phenyl-3-(p-dimethylaminophenyl)pyrazoline, hydrazone compounds,triphenylamine compounds, indole compounds, oxazole compounds,iso-oxazole compounds, thiazole compounds, thiadiazole compounds,imidazole compounds, pyrazole compounds, triazole compounds, and othernitrogen-containing cyclic compounds and fused polycyclic compounds.These charge transport materials can be used singly or in the form ofmixtures of two or more of them. Incidentally, in the case where afilm-forming charge transport material such as polyvinyl carbazole isused, use of a binder resin is not always necessary.

For example, a single-layer electrophotographic photosensitive materialis prepared by forming a photosensitive layer containing a compoundrepresented by general formula [I] as the charge transport material, acharge generating material and a binder resin on an electroconductivesubstrate. A laminate type electrophotographic photosensitive materialis prepared by forming a charge generating layer containing a chargegenerating material on an electroconductive substrate by such means asvacuum deposition or coating and forming a charge transport layercontaining a compound represented by general formula [I] and a binder onthe charge generating layer, or vice versa by forming a similar chargetransport layer on an electroconductive substrate and forming a chargegenerating layer containing a charge generating material on the chargetransport layer by such means as vacuum deposition or coating. Thecharge generating layer can also be prepared by dispersing a chargegenerating material and a charge transport material in a binder resinand coating the dispersion.

As the charge generating material, there can be mentioned, for example,selenium, selen-tellurium, amorphous silicon, a pyrylium salt, an azopigment, a disazo pigment, an anthanthrone pigment, a phthalocyaninepigment, an indigo pigment, a triphenylmethane pigment, a surenepigment, a toluidine pigment, a pyrazoline pigment, a perylene pigment,a quinacridone pigment and a pyrrole pigment. One or more of thesecharge generating materials can be used so that a desired absorptionwavelength region can be obtained.

As the binder resin for the above-mentioned photosensitive layer, chargegenerating layer and charge transport layer, various resins can be used.For example, there can be mentioned thermoplastic resins such as astyrene polymer, a styrene/butadiene copolymer, a styrene/acrylonitrilecopolymer, a styrene/maleic acid copolymer, an acrylic polymer, astyrene/acrylic copolymer, polyethylene, an ethylene/vinyl acetatecopolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene,a vinyl chloride/vinyl acetate copolymer, a polyester, an alkyd resin, apolyamide, a polyurethane, a polycarbonate, a polyallylate, apolysulfone, a diallyl phthalate resin, a ketone, a polyvinyl butyralresin and a polyether resin, crosslinkable thermosetting resins such asa silicone resin, an epoxy resin, a phenolic resin, a urea resin and amelamine resin, and photosetting resins such as epoxy acrylate andurethane acrylate. These binder resins can be used singly or in the formof mixtures of two or more of them.

A solvent is used when the charge generating layer or the chargetransport layer is formed by coating. For this purpose, various organicsolvents can be used. For example, there can be mentioned alcohols suchas methanol, ethanol, isopropanol and butanol, aliphatic hydrocarbonssuch as n-hexane, octane and cyclohexane, aromatic hydrocarbons such asbenzene, toluene and xylene, halogenated hydrocarbons such asdichloromethane, dichloroethane, tetrachloromethane and chlorobenzene,ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether and diethyleneglycol dimethyl ether, ketones such as acetone, methylethylketone andcyclohexanone, esters such as ethyl acetate and methyl acetate, anddimethylformamide and dimethylsulfoxide. These solvents can be usedsingly or in the form of mixtures of two or more of them.

In order to increase the sensitivity of the charge generating layer, aknown sensitizing agent such as terphenyl, a halonaphthoquinone oracenaphthylene can be used in combination with the above-mentionedcharge generating material. Moreover, a surface active agent, a levelingagent or the like can be used in order to improve the dispersibility orcoating property of the charge transport material or the chargegenerating material.

Various materials having an electroconductivity can be used as theelectroconductive substrate. For example, there can be mentioned metalssuch as aluminum, copper, tin, platinum, gold, silver, vanadium,molybdenum, chromium, cadmium, titanium, nickel, palladium, indium,stainless steel and brass, plastic materials on which theabove-mentioned metals are vacuum-deposited and laminated, and glasssheets coated with aluminum iodide, tin oxide, indium oxide or the like.The electroconductive substrate may be in the form of a sheet or a drum.A substrate which is electroconductive by itself or has anelectroconductive surface and which shows a sufficient strength when itis actually used is preferably used in the present invention.

The laminate type electrophotographic photosensitive material isprepared by coating a charge transport layer and a charge generatinglayer on an electroconductive substrate in this order (photosensitivematerial for negative charging) or in the reverse order (photosensitivematerial for positive charging).

The charge transport layer is formed by dissolving or dispersing acompound of general formula [I] singly or in combination with othercharge transport material in a binder resin to form a coating liquid andcoating and drying the coating liquid.

The compound of the present invention as the charge transport materialand the binder resin can be used at various ratios, so far as thetransportation of charges is not inhibited and the crystallization isnot caused. If the compound of the present invention is singly used asthe charge transport material, it is preferred that the compound ofgeneral formula [I] be used in an amount of 125 to 200 parts by weightper 100 parts by weight of the binder resin.

If the amount of the compound of general formula [I] is too small andbelow the above-mentioned range, a sufficient sensitivity cannot beobtained. If the amount of the compound of formula [I] is too large andexceeds the above-mentioned range, the crystallization is caused or thestrength of the layer is reduced.

It is preferred that the charge transport layer be formed in a thicknessof 2 to 100 μm, especially about 5 to about 30 μm.

In the case where the above-mentioned charge generating material is usedtogether with the binder resin for formation of the charge generatinglayer, they can be used at various ratios, but it is preferred that thebinder resin be used in an amount of 1 to 300 parts by weight,especially 5 to 150 parts by weight, per 10 parts by weight of thecharge generating material.

The thickness of the charge generating layer is not particularlycritical, but it is preferred that the charge generating layer be formedin a thickness of 0.01 to 20 μm, especially about 0.1 to about 10 μm.

For formation of the single-layer electrophotographic photosensitivematerial, the charge transport material and charge generating materialare used in amounts of 50 to 200 parts by weight and 3 to 10 parts byweight, respectively, per 100 parts by weight of the binder resin. Incase of the single-layer electrophotographic photosensitive material, itis preferred that the compound of the present invention represented bygeneral formula [I] be incorporated in an amount of at least 30 parts byweight per 100 parts by weight of all of the charge transport materialsand in an amount of at least 25 parts by weight per 100 parts by weightof the binder resin.

In the case where the compound of the present invention represented bygeneral formula [I] is used singly as the charge transport material, itis preferred that the compound of formula [I] be used in an amount of 70to 200 parts by weight per 100 parts by weight of the binder resin. Ifthe amount of the compound of general formula [I] is too small and belowthe above-mentioned range, a sufficient sensitivity cannot be obtained,and if the amount of the compound of formula [I] is too large andexceeds the above-mentioned range, the crystallization is caused and thestrength of the photosensitive layer is reduced, resulting indegradation of the printability.

In the formation of the photosensitive material, a barrier layer can beformed on the surface of the electroconductive substrate, so far as thecharacteristics of the photosensitive material are not degraded. Ofcourse, a protective layer can be formed on the surface of thephotosensitive material.

When the photosensitive layer is formed by the coating means, acomposition comprising the above-mentioned components at theabove-mentioned ratio is formed into a coating liquid by using knownmeans such as a roll mill, a ball mill, an attriter, a paint shaker oran ultrasonic disperser, and the coating liquid is coated and dried byknown coating means. Incidentally, as pointed out hereinbefore, thecharge generating layer can be formed by vacuum deposition of theabove-mentioned charge generating material.

The present invention will now be described in detail with reference tothe following examples that by no means limit the scope of theinvention.

REFERENTIAL EXAMPLE 1 [Synthesis ofN,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine]

In a nitrogen current, 11 g of resorcinol, 22.6 g of m-toluidine and 0.5g of iodine were reacted under reflux for 3 days. After the reaction,the reaction mixture was cooled to room temperature, and the formedsolid was washed with 500 ml of methanol to obtainN,N'-tetrakis(3-tolyl)-1,3-phenylenediamine. Then, 14.4 g ofN,N'-tetrakis(3-tolyl)-1,3-phenylenediamine 20.4 g of iodobenzene, 9.7 gof potassium carbonate and 2 g of powdery copper were reacted underreflux in 100 ml of nitrobenzene for 24 hours. After the reaction,nitrobenzene and iodobenzene were removed by stream distillation, andthe residue was washed with water and then with methanol. Then, theresidue was added into 900 ml of benzene. The water-soluble substancewas recovered by filtration and subjected to the active alumina columnchromatography using benzene/hexane (1/1) as the developing solvent. Thefirst fraction was recovered and subjected to the active alumina columnchromatography using benzene/hexane (1/2) as the developing solvent. Thefirst fraction was recovered and the solvent was removed bydistillation. A part of the residue was dissolved in acetonitrile atroom temperature, and by using the formed crystal as the seed,crystallization was carried out from acetonitrile to obtainN,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine (meta-substitutedcompound).

REFERENTIAL EXAMPLE 2 [Synthesis ofN,N,N',N'-tetrakis(4-tolyl)-1,3-phenylenediamine]

N,N'-Tetrakis(4-tolyl)-1,3-phenylenediamine was synthesized in the samemanner as described in Referential Example 1 except that 22.6 g ofp-toluidine was used instead of m-toluidine used in ReferentialExample 1. Then, 14.4 g of N,N'-tetrakis(4-tolyl)-1,3-phenylenediamine,21.8 g of iodotoluene, 9.7 g of potassium carbonate and 2 g of powderycopper were reacted under reflux in 100 ml of nitrobenzene for 24 hours.After the reaction, nitrobenzene and iodobenzene were removed by steamdistillation, and the residue was washed with water and then withmethanol. The residue was added into 900 ml of benzene, and thewater-soluble substance was recovered by filtration and subjected to theactive alumina column chromatography using benzene/hexane (1/1) as thedeveloping solvent. The first fraction was recovered and subjected tothe active alumina column chromatography using benzene/hexane (1/2) asthe developing solvent. The first fraction was recovered and the solventwas removed by distillation, and a part of the residue was dissolved inacetonitrile at room temperature. By using the formed crystal as theseed, crystallization was carried out from acetonitrile to obtainN,N,N',N'-tetrakis(4-tolyl)-1,3-phenylenediamine (para-substitutedcompound).

The preparation of the electrophotographic photosensitive material willnow be described.

EXAMPLE 1

A dispersion was prepared from 8 parts by weight ofN,N'-di(3,5-dimethylphenyl)perylene-3,4,9,10-tetracarboxydiimide as thecharge generating material, 125 parts by weight ofN,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine (meta-substitutedcompound) as the charge transport material, 100 parts by weight of apolycarbonate Z resin as the binder resin and a predetermined amount oftetrahydrofuran by using an ultrasonic disperser. The dispersion wascoated on an alumite-treated aluminum sheet to form a single-layerelectrophotographic photosensitive material comprising a photosensitivelayer having a thickness of 23 μm.

EXAMPLE 2

A single-layer electrophotographic photosensitive material was preparedin the same manner as described in Example 1 except that 150 parts byweight of N,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine(meta-substituted compound) was used as the charge transport material.

EXAMPLE 3

A single-layer electrophotographic photosensitive material was preparedin the same manner as described in Example 1 except that 200 parts byweight of N,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine(meta-substituted compound) was used as the charge transport material.

EXAMPLE 4

In 2000 parts by weight of dichloromethane were incorporated 100 partsby weight of polyvinyl butyral(Denka Butyral #500-A supplied by DenkiKagaku Kogyo) and 100 parts by weight of the same perylene type pigmentas used in Example 1, and the mixture was subjected to ultrasonicdispersing for 1 minute to prepare a coating liquid for formation of acharge generating layer. The coating liquid was coated and dried on analuminum sheet to form a charge generating layer having a thickness ofabout 1 μm.

Separately, 100 parts by weight of a polycarbonate Z resin (supplied byMitsubishi Gas Kagaku) and 125 parts by weight of the same chargetransport material (metasubstituted compound) as used in Example 1 weredissolved in 900 parts by weight of tetrahydrofuran to form a coatingliquid for formation of a charge transport layer. The coating liquid wascoated and dried on the charge generating layer to form a chargetransport layer having a thickness of about 20 μm, whereby a laminatetype photosensitive material was obtained.

COMPARATIVE EXAMPLE 1

A single-layer electrophotographic photosensitive material was preparedin the same manner as described in Example 1 except that 90 parts byweight of N,N,N',N'-tetrakis(4-tolyl)-1,3-phenylenediamine(para-substituted compound) was used as the charge transport material.

COMPARATIVE EXAMPLE 2

A single-layer electrophotographic photosensitive material is preparedin the same manner as described in Example 1 except that 100 parts byweight of N,N,N',N'-tetrakis(4-tolyl)-1,3-phenylenediamine(para-substituted compound) was used as the charge transport material.

COMPARATIVE EXAMPLE 3

A single-layer electrophotographic photosensitive material was preparedin the same manner as described in Example 1 except that 90 parts byweight of N,N,N',N'-tetrakis-phenyl-1,3-phenylenediamine (unsubstitutedcompound) was used as the charge transport material.

COMPARATIVE EXAMPLE 4

A single-layer electrophotographic photosensitive material was used inthe same manner as described in Example 1 except that 100 parts byweight of diethylaminobenzaldehyde diphenylhydrazone was used as thecharge transport material.

The electrophotographic photosensitive materials prepared in theforegoing examples were evaluated in the following manner.

With respect to the charging and photosensitive characteristics, eachphotosensitive material was positively or negatively charged by using anelectrostatic copying tester (Gentec Synthia 30M supplied by Gentec) andthe surface potential Vsp (V) was measured, and by using a halogen lamp,each photosensitive material was exposed to light, the time required forreduction of the surface potential to 1/2 was measured and thehalf-value exposure quantity E1/2 (μJ/cm²) was calculated, while thesurface potential Vrp (V) after the lapse of 0.15 second from the pointof termination of the light exposure was measured. Moreover, withrespect to each photosensitive material, the crystallization state wasexamined with the naked eye and it was checked whether or not thecrystallization was caused.

The results of the measurement of the charging and photosensitivecharacteristics of the electrophotographic photosensitive materialsobtained in the foregoing examples are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                       E1/2                Crystal-                                          Vo (V)  (μJ/cm.sup.2)                                                                        Vrp (V)   lization                                   ______________________________________                                        Example 1                                                                              660       25.2      129     not found                                Example 2                                                                              660       17.0      112     not found                                Example 3                                                                              650       19.4      112     not found                                Example 4                                                                              -660      23.5      -98     not found                                Comparative                                                                            --        --        --      caused                                   Example 1                                                                     Comparative                                                                            --        --        --      caused                                   Example 2                                                                     Comparative                                                                            650       27.8      135     not found                                Example 3                                                                     Comparative                                                                            640       33.6      163     not found                                Example 4                                                                     ______________________________________                                    

From the results shown in Table 2, it is seen that in each of theelectrophotographic photosensitive materials obtained according to thepresent invention, charging characteristics were excellent with nocrystallization, the half-value light exposure quantity was small, thesensitivity was high and the residual potential was small. In thephotosensitive materials of Comparative Examples 1 and 2, thecrystallization was caused. In the photosensitive material ofComparative Example 3 where the unsubstituted compound was used andphotosensitive material of Comparative Example 4 where the conventionalhydrazone compound was used, the sensitivity was lower and the residualpotential was larger than in the photosensitive materials of the presentinvention.

When the unsubstituted diamine compound (Comparative Example 4) wasincorporated in an increased amount as in Examples 1, 2 and 3, thecrystallization was readily caused in the photosensitive layer.

From the foregoing experimental results, it was confirmed that use ofthe meta-substituted compound of the present invention is very effectiveand advantageous.

As is apparent from the foregoing description, since themeta-substituted m-phenylenediamine compound of the present invention ishardly crystallized in a resin but is sufficiently dissolved in theresin, the concentration of the compound in the resin can be increasedand the mobility can be enhanced. Accordingly, an electrophotographicphotosensitive material having an increased sensitivity can be obtained.

We claim:
 1. An electrophotographic photosensitive material containingin a photosensitive layer an m-phenylenediamine compound represented bythe following general formula [I]: ##STR5## wherein R⁵, R⁶, R⁷ and R⁸are groups substituted at meta-positions to the nitrogen atoms andrepresent a hydrogen atom, an alkyl group, an alkoxyl group or a halogenatom, with the proviso that at least two of R⁵, R⁶, R⁷ and R⁸ representan alkyl group, alkoxyl group or a halogen atom, and R represents ahydrogen atom, an alkyl group, an alkoxyl group or a halogen atom.
 2. Anelectrophotographic photosensitive material as set forth in claim 1,wherein the photosensitive layer is formed by incorporating a chargegenerating material and a charge transport material in a binder resin,and the m-phenylenediamine compound represented by general formula [I]is used as the charge transport material.
 3. An electrophotographicphotosensitive material as set forth in claim 2, wherein them-phenylenediamine compound is incorporated in an amount of 25 to 200parts by weight per 100 parts by weight of the binder resin.
 4. Anelectrophotographic photosensitive material as set forth in claim 2,wherein the charge generating material is incorporated in an amount of 3to 10 parts by weight per 100 parts by weight of the binder resin.
 5. Anelectrophotographic photosensitive material as set forth in claim 1wherein the m-phenylenediamine compound of formula (I) is one of thecompounds set forth in Table 1 in the specification.
 6. Anelectrophotographic photosensitive material according to claim 1 whereinsaid photosensitive layer comprises the m-phenylenediamine compound offormula (I) in a binder resin wherein the amount of the compound offormula (I) is from 125 to 200 parts by weight per 100 parts by weightof the binder resin.
 7. An electrophotographic photosensitive materialas set forth in claim 1 wherein the m-phenylenediamine compound isN,N,N',N'-tetrakis(3-tolyl)-1,3-phenylenediamine.